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Title: EXTraS discovery of an 1.2-s X-ray pulsar in M 31
Authors: Esposito, P.
Israel, G. L.
Belfiore, A.
Novara, G.
Sidoli, L.
Rodríguez Castillo, G. A.
De Luca, A.
Tiengo, A.
Haberl, F.
Salvaterra, R.
Read, Andrew M.
Salvetti, D.
Sandrelli, S.
Marelli, M.
Wilms, J.
D'Agostino, D.
First Published: 31-Dec-2015
Publisher: Oxford University Press (OUP)
Citation: Monthly Notices of the Royal Astronomical Society Letters, 2015, 457 (1): L5-L9.
Abstract: During a search for coherent signals in the X-ray archival data of XMM–Newton, we discovered a modulation at 1.2 s in 3XMM J004301.4+413017 (3X J0043), a source lying in the direction of an external arm of M 31. This short period indicates a neutron star (NS). Between 2000 and 2013, the position of 3X J0043 was imaged by public XMM–Newton observations 35 times. The analysis of these data allowed us to detect an orbital modulation at 1.27 d and study the long-term properties of the source. The emission of the pulsar was rather hard (most spectra are described by a power law with Γ < 1) and, assuming the distance to M 31, the 0.3–10 keV luminosity was variable, from ∼3 × 1037 to 2 × 1038 erg s−1. The analysis of optical data shows that, while 3X J0043 is likely associated to a globular cluster in M 31, a counterpart with V ≳ 22 outside the cluster cannot be excluded. Considering our findings, there are two main viable scenarios for 3X J0043: a peculiar low-mass X-ray binary, similar to 4U 1822−37 or 4U 1626−67, or an intermediate-mass X-ray binary resembling Her X−1. Regardless of the exact nature of the system, 3X J0043 is the first accreting NS in M 31 in which the spin period has been detected.
DOI Link: 10.1093/mnrasl/slv194
ISSN: 1745-3925
eISSN: 1745-3933
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. The file associated with this record is distributed under the Creative Commons “Attribution Non-Commercial No Derivatives” licence, further details of which can be found via the following link:
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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